1. Field of the Invention
This invention relates generally to the data processing field and more particularly to a system management facility directly coupled to a system bus and providing centralized resources for controlling the data processing unit which includes tightly coupled central subsystems.
2. Description of the Prior Art
Any data processing system includes a means for providing some external control of the system. A system having a single central processing unit would typically have a control panel with switches to turn power on and off, to boot the system and to set information into registers. The control panel would also have lights to indicate the power status and the contents of registers. Also included are usually a single cycle switch and a single instruction switch. Later systems provided a console cathode ray tube display terminal to provide these functions.
As the data processing requirements increased, dual processors were used. The operator panel or display terminal was coupled to one of the processors, which became a master. In the event of a problem with the master processor, another processor could become the master.
As the reliability of data processing systems improved, the user did not need the cost of dedicated personnel to debug hardware or software problems. Manufacturers therefore provided systems with a remote maintenance capability, that is, maintenance personnel could operate from a central site and communicate directly with data processing systems by transferring data over phone lines using modems at the data processing site and the central site. A typical system is described in the Honeywell Tacdial Remote Users Guide, order number VF16-01, May 1983. The typical system includes a number of central subsystems, a main memory and a number of peripheral controllers, all coupled in common to a system bus. Coupled directly to one of the central subsystems is a system control facility. Coupled to the system control adapter is a remote maintenance display terminal, a local display terminal and an auxiliary device, typically a logging printer.
The central subsystem to which the system control facility is coupled becomes the master. The master central subsystem receives all of the control information from the system control facility and communicates that control information to the other subsystems over the system bus.
The individual subsystems perform their quality logic tests (QLT) under control of the master central subsystem which in turn reports the results to the system control facility.
Each central subsystem also has a watch dog timer and a real time clock controlling the software procedures.
The coupling of the system control facility to the master central subsystem limits it as a maintenance tool since it is fully operational only if the master central subsystem is operating properly. Its ability to test for malfunctions in the master central subsystems is very limited.
Also, the system control facility cannot obtain access to the system bus quickly in case of a power alert, but rather, has to wait for the master central subsystem to access the bus. Since the master central system has lower priority than other subsystems, including memory subsystems and some peripheral subsystems, alerts may be delayed.
The overall system has the cost and overhead disadvantage of various kinds of resources being duplicated in separate subsystems. These resources include the system timers, the boot load and QLT control.